The present invention relates to a multi-stage rolling mill having work rolls of a small diameter and supporting rolls for supporting and driving the work rolls.
In order to roll thin or hard material smoothly while meeting the demand for saving energy used in driving the rolling mill, a rolling mill has been proposed in which small-diameter work rolls having bending means are combined with axially shiftable intermediate rolls with bending means and back-up rolls. Such a rolling mill is disclosed, for example, in the specification of the U.S. Pat. No. 4369646 (Japanese Patent Laid-Open Publication No. 66307/1981).
When work rolls of small diameter are used for smooth rolling of hard and thin material such as stainless steel sheet, it is not possible to directly transmit the driving torque to the work rolls due to restrictions in terms of mechanical strength. In such a rolling mill, therefore, the driving torque is transmitted to the intermediate rolls which in turn transmit the driving torque to the small work rolls thus effecting the rolling. In this case, since the intermediate rolls are driven in the direction counter to the small work rolls, the small work rolls are urged by a horizontal force F.sub.H in the direction opposite to the direction of running of the rolled material, due to the friction between the intermediate rolls and the small work rolls and the friction between the small work rolls and the rolled material. This horizontal force F.sub.H tends to deflect the small work roll horizontally towards the material inlet side of the rolling mill, which in turn causes marks known as "Herringbone marks" to appear on the surface of the rolled material. This inconveniently degrades the quality of the rolled product and impairs the shape of the same.
Various proposals have been made to overcome this problem. For instance, it has been proposed to support the work roll surface both from the material inlet and outlet sides such as to prevent deflection of the small work rolls towards the material inlet side. According to another proposal, the work roll surface is supported from the material outlet side and, at the same time, the work roll is positively displaced at suitable points selected along the axis such as to effect a shape control of the rolling.
These methods, however, cannot perfectly prevent the deflection of the small work rolls stably, and cannot satisfactorily meet the demand for both the smooth rolling of harder material into smaller thicknesses and the saving of driving energy.
More specifically, the method in which the small work roll is supported both from the material inlet and outlet sides, disclosed in the specification of the U.S. Pat. No. 4270377 (Japanese Patent Laid-Open Publication No. 30390/1980), employs horizontal support rolls for horizontally supporting the work roll. The horizontal supporting rolls are carried by respective frames the positions of which are adjustable through rotation of the adjusting screws. Such an arrangement is quite unsuitable for quick positioning of the horizontal supporting rolls. In addition, the positioning of the small work roll correctly at the position for preventing the horizontal bending of the small work rolls is difficult because of the presence of play between the adjusting screws and the frame. In addition, this method is inconvenient from the view point of easiness of roll replacement which is often essentially conducted in rolling mills. The replacement of the work rolls requires a working space around the work roll. When horizontal supporting rolls are used, therefore, it is necessary to quickly move these horizontal work rolls out of contact with the work roll to afford such working space. In the known system of the type described, the movement of the horizontal suporting rolls is possible only through the operation of the adjusting screw as in the case of the positioning of the horizontal supporting rolls. Consequently, much labour and time are required for the roll replacement, resulting in a lower rate of operation of the rolling mill. In the case where chocks having a roll bending means are used in combination with the work rolls, the above-mentioned working space has to be considerably large in order to accommodate not only the work rolls pulled out from the working position but also the chocks which have a size much greater than that of the work roll. With the above-explained known system, lacking such a large working space, it is totally impossible to replace the work roll combined with a roll bending means carried by a large chock.